rxjs: Build error when using rxjs-compat: All declarations of 'observable' must have identical modifiers.

Bug Report

Current Behavior A clear and concise description of the behavior. ERROR in node_modules/rxjs/internal/symbol/observable.d.ts(4,9): error TS2687: All declarations of ‘observable’ must have identical modifiers. node_modules/@types/node/index.d.ts(167,14): error TS2687: All declarations of ‘observable’ must have identical modifiers.

Reproduction After installing rxjs 6.2.0 and rxjs-compat 6.2.0, navigate to ‘/node_modules/rxjs/internal/symbol/observable.d.ts’ and ‘./node_modules/@types/node/index.d.ts’

The IDE will indicate the error line readonly observable: symbol;

[ts] All declarations of 'observable' must have identical modifiers.
(property) SymbolConstructor.observable: symbol

Expected behavior The source code has error when using IDE to inspect.

The error should not appear. Environment

• Runtime: [e.g. Node v10.2.1, VSCode 1.23.1
• RxJS version: 6.2.0

Additional context/Screenshots Add any other context about the problem here. If applicable, add screenshots to help explain. https://imgur.com/a/eMdeN6k